\input pstricks.tex
\input pst-node.tex
\nopagenumbers
$
\psset{linewidth=0.8pt,labelsep=0.5ex,unit=2em}
\pcline(0,0)(0,2)
\Aput{a}
\pcline(0,2)(5,2)
\pcline(5,2)(5,0)
\pcline(5,0)(0,0)
\Aput{b}
$
\bye
